People could join the "bad side", although in the end of that main arc they would have to "lose", although they'd be forgiven by most because that side seemed just as logical but in different ways up until a major plot twist is revealed. I'm not spoiling it, but it does explain why your guy being able to leave and all that wouldn't work up until then.

A) That's true for the main story arc as mentioned, but more free form plots would also be opened up both before then and then a ton after when the multiverse aspect kicks in to other planets.
B) You don't have to deal with them if you just want to start your roleplays after that point in the timeline. You don't even need your character to have taken part in it.
C) After that part in the timeline you wouldn't have to set one foot on that world if you're that stubborn. :lol

There wouldn't have to be a common goal at that point in the timeline. The world is opened up to the outside. Consider everything that happened before just backstory and after that point is where the actual multiverse.